An analog/digital mixed circuit is known in which an analog circuit and a digital circuit are disposed on one circuit. The analog circuit and the digital circuit are coupled together via a data converter such as an analog-to-digital converter (ADC) or a digital-to-analog converter (DAC) which is disposed on the same chip. For example, when the digital circuit and the DAC are disposed on the same chip, a fluctuation in a power supply voltage for the digital circuit may propagate to the DAC as power supply noise and degrade the resolution of the DAC.